The statement in the post is not quite right: neurons are negative at rest, and when they fire, their inside becomes positive relative to the outside , but the cell as a whole does not suddenly become a positively charged object in space.

Quick Scoop: What’s actually going on

When we say “neurons have a net negative charge at rest,” we are really talking about membrane potential – the voltage difference between the inside and outside of the cell, typically around −70 mV (inside is more negative).

During an action potential (when the neuron is “active” or “firing”):

  1. Voltage-gated sodium (Na⁺) channels open.
  2. Na⁺ rushes into the cell.
  3. The membrane potential swings from about −70 mV to about +30 mV, meaning the inside becomes more positive than the outside for a brief moment.

So the membrane potential goes from negative to positive, but that does not mean the neuron as a whole must now have a net positive charge in the sense of having more total positive charge than the surrounding world. It’s a local, small redistribution of ions across a thin membrane, not the neuron “charging up” like a positively charged balloon.

Fixing the reasoning in the post

The post’s reasoning:

“Neurons have a net negative charge at rest. This means that when they are active, they must have a positive charge.”

What’s correct:

  • At rest, the inside of a neuron is more negative than the outside (about −70 mV).
  • When active (during the peak of an action potential), the inside becomes positive relative to the outside (about +30 mV).

What’s misleading:

  • Saying they “must have a positive charge” suggests a kind of all-or-nothing flip of the whole neuron’s net charge, which isn’t how it works.
  • The important concept is the change in membrane potential (negative → positive relative difference), not the absolute total net charge of the entire cell.

A clearer version would be:

“Neurons have a negative membrane potential at rest. When they fire an action potential, the inside of the neuron briefly becomes positive relative to the outside.”

Mini sections: key points to highlight

1. Resting state

  • Inside is ~70 mV more negative than outside.
  • Caused by ion gradients (more K⁺ inside, more Na⁺ outside) and selective permeability, supported by the sodium–potassium pump.

2. Active state (action potential)

  • A stimulus opens voltage-gated Na⁺ channels.
  • Na⁺ rushes in, making the inside more positive than the outside (depolarization to around +30 mV).
  • Then K⁺ channels open, K⁺ flows out, and the neuron repolarizes back toward the negative resting potential.

3. Why “net positive neuron” is an overstatement

  • The voltage change is across a very thin membrane; only a tiny fraction of ions move.
  • The action potential is about relative inside-vs-outside charge, not the neuron becoming a big positively charged object overall.

Bottom note

Information gathered from public forums or data available on the internet and portrayed here.